In an existing TDD (time division duplex) system, there are seven uplink-downlink configurations shown in Table 1.
TABLE 1Downlink-Uplink-to-uplink downlinkswitch-point Subframe numberconfigurationperiodicity01234567890 5 msDSUUUDSUUU1 5 msDSUUDDSUUD2 5 msDSUDDDSUDD310 msDSUUUDDDDD410 msDSUUDDDDDD510 msDSUDDDDDDD6 5 msDSUUUDSUUD
In Table 1, downlink-to-uplink switch-point periodicity indicates an uplink-downlink switch period, subframe number indicates a subframe number, D indicates a downlink subframe, U indicates an uplink subframe, and S indicates a special subframe. The special subframe includes three parts, that is, a DwPTS (downlink pilot timeslot), a GP (guard period), and an UpPTS (uplink pilot timeslot). The GP is mainly used as compensation for a downlink-to-uplink switch time and for an uplink and downlink transmission delay. Particularly, the DwPTS in the special subframe may be used to transmit downlink data. Therefore, sometimes, the special subframe may be considered as a downlink subframe.
It may be learned from Table 1 that in the prior art, for the seven uplink-downlink configurations, seven frame structures of a radio frame are provided in total.
In an LTE (Long Term Evolution) system, to support hybrid automatic repeat, UE (user equipment) needs to feed back a HARQ-ACK (hybrid automatic repeat request-acknowledgment) of PDSCH (physical downlink shared channel) transmission to a base station by using a PUCCH (physical uplink control channel) and a PUSCH (physical uplink shared channel). The HARQ-ACK may also be simply indicated as an ACK (acknowledgment)/NACK (negative acknowledgement). The UE needs to receive, by using a PHICH (physical hybrid-ARQ indicator channel), the HARQ-ACK corresponding to the PUSCH.
In the prior art, in an FDD (frequency division duplex) system, a HARQ-ACK corresponding to a PDSCH transmitted at a downlink subframe n−4 is to be fed back at an uplink subframe n. In a TDD system, a HARQ-ACK corresponding to a PDSCH transmitted at a downlink subframe n−k is to be fed back at an uplink subframe n, where k belongs to a set K. Referring to Table 2, Table 2 defines K for different uplink-downlink configurations of a cell in the TDD system.
TABLE 2UL-DLconfig-Subframe nuration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6————8, 7, 4, 6——3——7, 6, 116, 55, 4—————4——12, 8, 7, 6, 5, ——————114, 75——13, 12, 9, ———————8, 7, 5, 4, 11, 66——775——77—
In Table 2, UL-DL configuration indicates an uplink-downlink configuration, and subframe n indicates a subframe. There are no corresponding values of k under some subframes, that is, there are hyphens (-), which indicate that these subframes are not used to transmit a HARQ-ACK.
It may be learned from Table 2 that values of k in the HARQ-ACK timing set K of the existing TDD system are all relatively large, leading to a relatively large service delay. In another aspect, in most uplink-downlink configurations, HARQ-ACKs of multiple subframes need to be fed back at one uplink subframe, leading to a complex HARQ-ACK feedback mechanism and relatively poor HARQ-ACK feedback performance.